1. Field of the Invention
The invention concerns an apparatus for localizing a focal lesion in a biological tissue section, the lesion exhibiting an electrical property different from the tissue section, and the electrical property in the tissue section being essentially constant, of the type having means to apply electrical excitation signals to the tissue section and with means to measure electrical response signals at a number of measurement locations on a surface of the tissue section that arise due to the excitation signals.
2. Description of the Prior Art
In imaging by means of electrical impedance, alternating voltages are applied to a tissue section to be examined at one or more locations, and/or electrical alternating currents are applied. Using measurement electrodes that are electrically contacted to the tissue section to be examined at a number of locations, currents (amplitude and phase) are measured that arise due to the applied voltages, and/or voltages (amplitude and phase) are measured that arise due to the applied currents and due to the electrical conductivity distribution of the subject. This method is at present used particularly for examination of lesions in a female breast.
An apparatus of the initially cited type is known from PCT Application WO 99/48422. The apparatus has a current or voltage source that is connected with electrodes. The current source (or the voltage source) generates a series of currents (or voltages) of different frequency that are supplied via the electrodes as excitation signals to a body section to be examined. Based on the excitation signals, lesions present within the body section generate response signals that are supplied to a measurement value-editing (or conditioning) unit via the aforementioned electrodes. The response signals are determined by the electrical properties (specified, for example, by a mathematically complex conductivity) of the subject having the lesion. The measurement value-editing unit is connected with a computer to which the edited measurement values and a model of the tissue section are supplied. From the edited measurement data and the model, the lesion is determined from the signal activity by means of a reconstruction method running on the computer, and its spatial position is determined.
For example, 64 or 256 time-dependent current values on the surface of a female breast can presently be measured with the commercially available device TS2000 from the company TransScan by means of 8×8 or 16×16 regularly arranged electrodes on a measurement surface of approximately 7.9×7.9 cm2. The current values arise as a result of an alternating voltage between measurement electrodes and a reference electrode held by the examination subject in the contralateral hand. The measurement data, (magnitude and phase of the current) are individually calculated as conductance and capacitance and are represented corresponding to the two-dimensional electrode arrangement.
If focal lesions that, for example, exhibit a higher electrical conductivity than the surrounding tissue, are located in the tissue section below the measurement electrodes, then (for example in the case of current measurements) higher current values are measured in the electrodes directly above them. Such a lesion is visible as a peak in the two-dimensional measurement data representation. The peak amplitude and the peak width depend on the size and depth of the lesion and on the conductivity difference between the lesion and the surrounding tissue.
The conductivities, in particular of breast tissue, are known both from the clinical practice and from tissue samples measured in vitro. The presence of a peak, however, still allows no clear conclusion about the malignity of the lesion.